The manufacturing facility of glass plate is provided for, e.g., the float method, the fusion method or the roll-out method. The manufacturing facility of glass plate for the float method is suitable for an effective manufacturing of large-size glass plate which is larger than one square meter.
The manufacturing facility of glass plate according to the float method will now be explained referring to drawings.
FIG. 1 is a schematic view of the manufacturing facility of glass plate according to the float method.
As shown in FIG. 1, in the manufacturing facility of glass plate according to the float method, a glass raw material charged from a material input port 1 is melted inside a glass melting furnace 2, and then is pushed out to become a molten glass 3. Then, the molten glass 3 spreads out into a float bath (tin bath) 5 filled with a molten tin 4, and becomes flattened. That is, when the molten glass 3 is introduced into the float bath 5 and is floated on the molten tin 4, the molten glass 3 is heated inside the float bath 5 by a heater 6 and thereby spreads out on the high-temperature molten tin 4. In detail, the molten glass 3 spreads spontaneously because of an equilibrium between a surface tension of molten glass 3 and a gravity, and thereby achieves a stable thickness of molten glass 3, in other words, achieves an equilibrium thickness.
As shown in FIG. 2, the molten glass 3 which has achieved the equilibrium thickness is lifted and pulled out by lift-out rolls 7. Then, the molten glass 3 is drawn and enlarged while the temperature of molten glass 3 is somewhat reduced, to become a glass ribbon G. Then, the glass ribbon G moves to the slow-cooling furnace 8.
As shown in FIGS. 1 and 2, normally, the slow-cooling furnace 8 is covered by a heat-insulation wall. The glass ribbon G which has moved into the slow-cooling furnace 8 is gradually cooled and conveyed by rotary drive of glass conveyance rolls 9, under a state where the glass ribbon G is located in contact with the glass conveyance rolls 9 inside the slow-cooling furnace 8. The glass ribbon G moves through a washing machine 10 and a drying machine 11 to a cutting machine 12. The glass ribbon G is cut into a desired size by the cutting machine 12, so that a desired glass plate is obtained.
Normally, a thickness of glass plate for building use such as a window glass is larger than or equal to 4.0 mm, and a conveying speed (moving speed) of this glass ribbon G is adjusted only by a rotational speed control of the glass conveyance rolls 9.
FIG. 3 is a horizontal cross-sectional view of one example of a manufacturing apparatus of glass plate according to the float method.
As shown in FIG. 3, in order to obtain the glass ribbon G which is thinner than its equilibrium thickness, normally, top rolls 13 press both width-directional end portions of the molten glass 3 in the float bath 5 so as to draw and enlarge the molten glass 3 in the width direction and thereby to thin the molten glass 3, as disclosed in a Patent Document 1. Each top roll 13 is formed with grooves and teeth, and presses the both width-directional end portions of molten glass 3 while being rotated by a motor 14 or the like.
For example, a Patent Document 2 discloses that each of the both end portions 15 of glass ribbon G given a tension by the top rolls 13 has a roll mark, and cannot be used for a product. Moreover, this Patent Document 2 discloses a method of relaxing a stress strain to reduce asperities of glass surface, by designing each of the both end portions 15 to have a degree of thickness equal to or slightly smaller than 3 mm which is thicker as compared with a glass ribbon's central portion having a thickness falling within a range from 0.1 mm to 1.5 mm and by designing each width of the both end portions 15 to be large.
Moreover, a Patent Document 3 written by the applicant of present application discloses a manufacturing method of float plate glass using the top rolls 13. This float plate glass is manufactured in order to be used for a substrate for plasma display, a substrate for liquid crystal display or the like.
The plasma display functions to display by causing lights at red, blue and green phosphors by means of electric discharge. Nowadays, a standard of thickness of the glass substrate for plasma display ranges from 1.8 mm to 2.8 mm. The liquid crystal display causes blinking of pixels by driving a liquid crystal panel by use of thin-film transistors (TFT system) or the like. The liquid crystal panel itself does not emit light, and needs backlight as its light source. A standard of thickness of the glass substrate for liquid crystal display is equal to 0.7 mm. Although the standard of thickness of the glass substrate for liquid crystal display was equal to 1.1 mm in past days, this standard has been developmentally changed to 0.7 mm in order to reduce a light leakage between pixels due to light interference and diffusion in the substrate, and in order to improve a resolution as liquid crystal panel and thereby to achieve a wide view angle. Moreover, a glass substrate which is used for a liquid crystal panel of mobile phone has a thickness equal to 0.4 mm as standard.
Moreover, as to the conveyance of glass ribbon inside the slow-cooling furnace and the like, a Patent Document 4 discloses a conveyance method of glass ribbon characterized as follows. In this glass-ribbon conveyance method, a high-temperature glass ribbon which is produced by the float method is taken out from a float bath and conveyed by conveyance rollers in order to prevent powdered tine, powdered glass and the like which are called “dross” from sticking to the glass ribbon from a melting bath, or in order to prevent a surface of glass ribbon from being scratched. Moreover, in this method, a suction lifting means for sucking the glass ribbon which has been taken out from the float bath, in a noncontact manner, to a space above the conveyance rollers is disposed so that the glass ribbon is conveyed under a state where all or part of the glass ribbon is lifted from the conveyance rollers. Thereby, the glass ribbon is conveyed by switching between a noncontact-conveyance operation of glass ribbon which is performed by the suction lifting means and a contact-conveyance operation of glass ribbon which is performed by the conveyance rollers, or by using the noncontact-conveyance operation in combination with the contact-conveyance operation, as needed basis.
Patent Document 1: Japanese Patent Application Examined Publication No. S44 (1969)-23828
Patent Document 2: Japanese Patent Application Publication No. H07 (1995)-10569
Patent Document 3: Japanese Patent Application Publication No. 2005-263602
Patent Document 4: Japanese Patent Application Publication No. 2000-239035